The blank frame and the block of 1020 from which I cut it.
The vertical bolt that works in unison with the underbolt, and makes it a rising bite action.
The frame after further machining. The right-side fence is rough chiseled to shape.
The top strap TIG welded in place.
The barrels contoured and fitted to the lump, and the top strap joint is refined. Also shown is the underbolt, vertical bolt, link and pivot as they are assembled in the frame. It's clear how the axial travel of the underbolt translates to the rising bolt's vertical travel via the link.
The right-side inboard mounted sidelock. The outside "lockplate" is simply a cover and obviously will be pinless. I'm going to incorporate a spring-loaded trapdoor in the outer lockplates to access the inner workings.
The cocking lever is also the mainspring. As the barrels open, the lever/spring rotates the tumbler to full cock where the sear will hold it. As the barrels are closed, the cam at the front will cramp the spring.
This also makes it a self-opener.
The lockplate, the bridle and the screws are 1020 (they will be case-hardened), the tumbler, sear, sear spring, mainspring and cocking cam are made of O1 (an oil hardening steel).
To give some idea of the amount of work involved, here is a photo of the lock bridle after machining the posts but before shaping it by hand.
I decided that the bridles should be pierced, in the interest of saving weight (not really).
With the locks sorted, it's time to make the triggerplate. Here's a shot of it early on.
Here is the triggerplate almost finished. Now I have to decide on a single trigger or double triggers.
I had originally planned on a single trigger but double triggers on a side-by-side do have a certain aesthetic appeal. I also decided against the sidelever, which I had considered, in favor of direct operation of the bolt via a slide in the forward portion of the triggerguard. This is similar in concept to what is used in the Ljutic Mono trap gun. It also allows the action to be completely symmetrical and ambidextrous.
I made a new, more functionally and aesthetically pleasing bolt slide and fabricated and welded the tang to the triggerguard.
Next was to make the left and right firing pin bushings, firing pins, springs and vent screws.
The blank for the forend iron with a portion of the bar of 1020 from which it was machined.
With the barrel breeches brazed, the barrels blacked down and the bolts fit, and the assembly proof-fired, I rewarded myself with some fun work. That work is chiseling the fences.